TS68HC901 datasheet(16/42 Pages) STMICROELECTRONICS

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ACTIVE EDGE REGISTER

AER

(03h)

GPIP7

GPIP6

GPIP5

GPIP4

GPIP3

GPIP2

GPIP1

GPIP0

1 = RISING

2 = FALLING

DATA DIRECTION REGISTER

DDR

(05h)

GPIP7

GPIP6

GPIP5

GPIP4

GPIP3

GPIP2

GPIP1

GPIP0

1 = OUTPUT

2 = INPUT

GENERAL PURPOSE I/O DATA REGISTER

GPIP

(01h)

GPIP7

GPIP6

GPIP5

GPIP4

GPIP3

GPIP2

GPIP1

GPIP0

Figure 11 :

Note

The transition detector is an exclusive-OR gate

whose inputs are the edge bit and the input buffer.

As a result, writing the EAR may cause an interrupt-

producing transition, depending upon the state of

the input. So, the AER should be configured before

enabling interrupts via the interrupt enable registers

(IERA and IERB). Also, changing the edge bit while

interrupts are enabled may cause an interrupt on the

corresponding channel.

DATA DIRECTION REGISTER

The data direction register (DDR) allows the pro-

grammer to define I0 through I7 as inputs or outputs

by writing the corresponding bit. When a bit of the

data direction register is written as a zero, the cor-

responding interrupt I/O pin will be a high-impe-

dance input. Writing a one to any bit of the data di-

rection register will cause the corresponding pin to

be configured as a push-pull output.

TS68HC901

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